The invention relates to a method and an apparatus for separation of mixtures of substances by means of flotation and/or sedimentation.
Such separation processes are widely used in ore processing to separate the ore from dead rock and in the paper industry to recover fibre components from white water or waste paper pulp.
In these methods, the mixture of substances to be separated is fed into a container which includes the separation agent (water in most cases) and in which the mixture separates to form a flotation concentrate which is collected at the surface and/or a sediment which settles at the bottom of the container.
By appropriately shaping the container and providing suitable installations, the separation agent released from the mixture by the above process can be extracted from the container in a substantially clean form and re-used.
It is also known that flotation and sedimentation processes can be enhanced by selecting appropriate flow conditions for the separation agent and by adding chemicals which adapt the process to individual substances or may result in a flocculation of substances to be floated.
Particularly short flotation times and improved results for specific substances can be obtained by gas flotation wherein the mixture containing the substances to be separated and the separation agent is saturated by pressurised gas (mostly air). When the pressure is released the gas forms small bubbles which will more rapidly carry components of the mixture to the surface.
U.S. Pat. No. 5,055,184 discloses embodiments of a separation tank and apparatus which render the discharge of the flotation and/or sedimentation concentrate particularly easy.
All known flotation and sedimentation methods have the disadvantage that parameters of the separation agent which influence the process cannot be altered once the process has started unless chemicals are added which, however, result in undesired residues in the flotation or sedimentation concentrate.
For this reason, the range of application of the known processes is limited and largely unsuited for separating biological substances and foodstuffs.
For food, there is the further difficulty that known apparatus use water as the separation agent, which alters the consistency of the mixture components or may not be separated from them in an economic way. When minced meat is processed to remove undesired fat or cartilage components, it may not be sold as "meat" but only as a "meat product" according to German food regulations. This involves substantial economical losses. The same is true with many natural substances and other complex mixtures of substances. When water is used as a separation agent, cooling to temperatures below 0.degree. C., as is required for some separation processes, is impossible.